The short answer is yes. You can store worm castings in the winter outside in the snow or in a container, bag, mesh Grow-Bag or anything.

It's best to cover it with something or even bury it a bit down in the ground. When spring arrives the microbes will awaken and be ready for use.

I keep all my indoor mature worm castings ACTUALLY INDOORS in a breathable Rubbermaid (or equivalent) container. I keep a small handful of a worms in the container to help refine the castings and keep it as fresh as possible.

I store at room temperature and stir it up with my hand once a month to keep the material from becoming stagnant in case some worms don't get to every part of the material.

All of this is not necessary, but helps in keeping the worm castings at its most potent and beneficial state for plant food as possible.

Keeping the microbes alive is better than dormant. This is why I always leave a few stragglers (worms) in the harvested castings.

There's still plenty of food in the castings for the few worms that remain.

If you have ANY other organism like mites or springtails, they'll not last long as there isn't any of their food sources in the mature/harvested castings.